Pattern forming method, electronic device manufacturing method and electronic device

ABSTRACT

On a film as an object of processing, a first positive photo-resist having a dense hole pattern is formed. On the first positive photo-resist, a second positive photo-resist is formed to fill each of the plurality of holes of the pattern. To the second photo-resist, an image of dark points as a bright-dark inverted image of a high-transmittance half-tone phase shift mask is projected and exposed. By the development of second photo-resist, a pattern of dots of the second photo-resist formed at portions of the dark point image are left in any of the plurality of holes of the pattern. The film as the object of processing is patterned, using the first and second photo-resists as a mask.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pattern forming method, an electronicdevice manufacturing method and to an electronic device. Morespecifically, the present invention relates to a method of forming arandomly arranged hole pattern having minute, isolated hole pattern, amethod of manufacturing an electronic device and to the electronicdevice.

2. Description of the Background Art

Formation of a hole pattern by photolithography requires, different froma line pattern, local presence of electromagnetic field when viewed twodimensionally. Therefore, miniaturization is difficult in principle.Further, when a pattern of holes is formed by a positive photo-resist,effective image contrast inherently becomes smaller.

Particularly, formation of a minute, isolated hole with high processmargin is difficult, as effective super-resolution technique has notbeen known. Therefore, formation of a minute, isolated hole remains onefactor hindering device miniaturization.

Because of the above-described limitation in principle, an optical imageformed by a pattern of regularly arranged holes has image qualityinferior to that of a pattern of dense lines that is a one-dimensionalpattern. For such a hole pattern, however, super-resolution techniquerepresented by modified illumination method is available. Therefore, byapplying a high-resolution photo-resist having superior separationperformance, minute holes of high density can be formed with highprocess margin.

In contrast, when a dark point image is formed, excellent image qualityof a pattern of random arrangement can be attained by applying aphase-cancellation image using a phase shift mask under optimallymodified illumination, as disclosed by the inventors of the presentinvention (see References 1 and 2 below).

Reference 1: Japanese Patent Laying-Open No. 2004-251969

Reference 2: S. Nakao et al., “Zero MEF Hole Formation with Atten-PSMand Modified Illumination”, Proc. of SPIE Vol. 5040 (2003), pp.1258-1269

Conventional formation of a pattern of randomly arranged holes byapplying a phase-inverted image using the phase shift mask requires anegative photo-resist, as described above. For the state-of-the-art ArFexcimer laser exposure, however, there is no negative photo-resist ofexcellent performance. Therefore, it has been difficult by theconventional method to realize characteristics sufficient for practicaluse with the wavelength of ArF excimer laser.

SUMMARY OF THE INVENTION

The present invention was made in view of the foregoing and its objectis to provide a pattern forming method, allowing formation of a patternof randomly arranged holes with high margin while applying a positivephoto-resist, an electronic device manufacturing method and theelectronic device.

The pattern forming method in accordance with an embodiment of thepresent invention includes the following steps.

First, on a film as the object of processing, a mask layer having apattern of dense holes with a plurality of densely positioned holes isformed by pattern formation applying a first positive photo-resist. Onthe mask layer, a second positive photo-resist is formed to fill each ofthe plurality of holes of the dense hole pattern. To the second positivephoto-resist, an image of dark points is projected and exposed, using ahalf-tone phase shift mask. By developing the exposed second positivephoto-resist, a pattern of dots formed on the portions corresponding todark points of the image of the second positive photo-resist is left inany of the plurality of holes of the pattern of the mask layer. Usingthe dot pattern (resist plug) formed by the mask layer and the secondpositive photo-resist as a mask, the film as the object of processing ispatterned. The half-tone phase shift mask has a half-tone phase shiftfilm having openings for generating dark point image for the dotpattern. The step of projecting and exposing the dark point image usingthe half-tone phase shift mask on the second positive photo-resistincludes the step of exposing with such an amount of exposure that thesecond positive photo-resist is dissolved at the time of developmentwith the intensity of exposure light transmitted through the half-tonephase shift mask in a region free of any opening, while the secondpositive photo-resist is not dissolved at the time of development withthe intensity of light at the dark point image formed by the openings atthe dot pattern portions.

According to the embodiment of the present invention, a pattern of denseholes is formed in the mask layer, which may be realized by using apositive photo-resist. Further, a pattern of randomly arranged dots intwo-dimensional view may be formed by using the positive photo-resist.Therefore, by forming the dense hole pattern in the mask layer andthereafter filling any of the dense holes of the pattern with the dotsof the pattern, a pattern of holes randomly arranged when viewedtwo-dimensionally can be formed using a positive photo-resist.Therefore, it becomes possible to form, with high margin, a pattern ofrandomly arranged holes by applying a positive photo-resist.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart representing a method of forming a pattern commonto Embodiments 1 to 4 of the present invention.

FIG. 2 is a flowchart specifically showing step S1 of FIG. 1, when themask layer is a positive photo-resist.

FIGS. 3 to 11 are schematic cross-sectional views showing, in order,steps of the pattern forming method in accordance with Embodiment 1.

FIG. 12 is a plan view showing a shape of a pattern formed on thehalf-tone phase shift mask of the photo mask used in the first exposureprocess.

FIG. 13 is a plan view showing a shape of a pattern formed on thehalf-tone phase shift mask of the photo mask used in the second exposureprocess.

FIG. 14 schematically shows an arrangement of a projection aligner usedin the first and second exposure processes in the pattern forming methodin accordance with Embodiment 1 of the present invention, particularlyillustrating the second exposure process.

FIG. 15 illustrates normal illumination.

FIG. 16 illustrates modified illumination.

FIG. 17 is a plan view showing an example of illumination diaphragm usedfor cross-pole illumination.

FIG. 18 is a plan view showing an example of illumination diaphragm usedfor quadrupole illumination.

FIG. 19 is a plan view schematically showing a structure of anelectronic device in accordance with Embodiment 1 of the presentinvention.

FIG. 20 shows intensity of an optical image formed by an image formingsystem when an opening of a high-transmission half-tone phase shift maskshown in FIG. 8 is provided as an isolated pattern having the dimensionof W=280 nm.

FIG. 21 shows intensity of an optical image formed by an image formingsystem when an opening of a high-transmission half-tone phase shift maskshown in FIG. 8 is provided as an isolated pattern having the dimensionof W=200 nm.

FIG. 22 shows intensity of an optical image formed by an image formingsystem when an opening of a high-transmission half-tone phase shift maskshown in FIG. 8 is provided as an isolated pattern having the dimensionof W=120 nm.

FIG. 23 shows intensity of an optical image formed by an image formingsystem when an opening of a high-transmission half-tone phase shift maskshown in FIG. 8 is provided as an isolated pattern having the dimensionof W=40 nm.

FIG. 24 is a contour line map representing intensity distribution of anoptical image of a pattern of 112 nm×112 nm holes arranged densely intwo-dimension with a pitch of 160 nm, formed under prescribed opticalconditions on a 20% transmittance half-tone phase shift mask, in thefirst exposure process.

FIG. 25 represents optical intensity distribution at positions along amain cross-section of the dense holes in the first exposure process,using focus as a parameter.

FIG. 26 plots dimension of bright point image formed in the firstexposure process, that is, Image CD with respect to the focus, usingslice level as a parameter.

FIG. 27 is a contour line map representing intensity distribution of anoptical image of a pattern of 62 nm×62 nm holes formed under prescribedoptical conditions on a 20% transmittance half-tone phase shift mask, inthe second exposure process.

FIG. 28 is a contour line map representing intensity distribution of anoptical image of a pattern of 62 nm×62 nm holes formed under prescribedoptical conditions on a 20% transmittance half-tone phase shift mask 30,in the second exposure process.

FIG. 29 plots optical image intensity at portions free of any hole ofthe mask used in the second exposure process, using focus as aparameter.

FIG. 30 plots optical image intensity at portions with isolated hole ofthe mask used in the second exposure process, using focus as aparameter.

FIG. 31 is a contour line map representing intensity distribution of anoptical image of a pattern of 88 nm×88 nm holes arranged densely intwo-dimension with a pitch of 120 nm, formed under prescribed opticalconditions on a 20% transmittance half-tone phase shift mask 20, in thefirst exposure process.

FIG. 32 represents optical intensity distribution at positions along amain cross-section of the dense holes in the first exposure process,using focus as a parameter.

FIG. 33 plots dimension of bright point image formed in the firstexposure process, that is, Image CD with respect to the focus, usingslice level as a parameter.

FIG. 34 is a contour line map representing intensity distribution of anoptical image of a pattern of 54 nm×54 nm holes formed under prescribedoptical conditions on a 20% transmittance half-tone phase shift mask 30,in the second exposure process.

FIG. 35 is a contour line map representing intensity distribution of anoptical image of a pattern of 54 nm×54 nm holes formed under prescribedoptical conditions on a 20% transmittance half-tone phase shift mask 30,in the second exposure process.

FIG. 36 plots optical image intensity at portions free of any hole ofthe mask used in the second exposure process, using focus as aparameter.

FIG. 37 plots optical image intensity at portions with isolated hole ofthe mask used in the second exposure process, using focus as aparameter.

FIG. 38 is a flowchart specifically representing step S1 of FIG. 1 whenthe mask layer is a hard mask layer.

FIGS. 39 to 49 are schematic cross-sectional views showing, in order,steps of the pattern forming method in accordance with Embodiment 3.

FIG. 50A includes a plan view showing the shape of a diaphragm ofannular illumination to find optimization of illumination shape forsquare lattice arrangement and optical intensity distribution forvarious pattern shapes of the photo mask shown in FIG. 8, using focus asa parameter.

FIG. 50B includes a plan view showing the shape of a diaphragm ofcross-pole illumination to find optimization of illumination shape forsquare lattice arrangement and optical intensity distribution forvarious pattern shapes of the photo mask shown in FIG. 8, using focus asa parameter.

FIG. 50C includes a plan view showing the shape of a diaphragm ofquadrupole illumination to find optimization of illumination shape forsquare lattice arrangement and optical intensity distribution forvarious pattern shapes of the photo mask shown in FIG. 8, using focus asa parameter.

FIG. 51 is a schematic plan view showing isolated pattern and densepattern mixed in a phase shift mask in accordance with an embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the figures.

Embodiment 1

Referring to FIG. 1, in the pattern forming method of the presentembodiment, first, on a film as the object of processing, a mask layerhaving a pattern of dense holes is formed (step S1). To fill the patternof dense holes, a positive photo-resist is formed on the mask layer(step S2). To the positive photo-resist, an image of dark points as abright-dark inverted image provided by a high-transmittance half-tone(HT) phase shift mask is projected and exposed (step S3). Structure ofthe high-transmittance half-tone phase shift mask capable of forming theimage of dark points as the bright-dark inverted image will be describedlater. The exposed positive photo-resist is developed. Thus, thepositive photo-resist is removed at portions other than the dot patternformed in the dark point image portion. Further, the positivephoto-resist at the dot pattern portion is left inside any of theplurality of holes forming the dense pattern, to serve as a resist plug(step S4). Using the positive photo-resist and the mask layer as a mask,the film as the object of processing is selectively removed andpatterned (step S5). In this manner, a pattern of holes arranged atrandom when viewed two-dimensionally is formed on the film.

Next, an example in which the mask layer is a positive photo-resist willbe described specifically.

Referring to FIG. 3, first, a film 2 as the object of processing isformed on a substrate (such as a wafer) 1.

Referring to FIG. 4, on the film 2 as the object of processing, a firstpositive photo-resist 3 is applied and formed (step S11: FIG. 2). Atthis time, though not shown, a bottom anti-reflection coating (BARC) anda top anti-reflection coating (TARC) are formed as upper and lowerlayers of the first positive photo-resist 3, as needed.

Referring to FIG. 5, the first exposure process is performed. An opticalimage of a half-tone phase shift mask 20 having a pattern of dense holesformed therein is projected to the first positive photo-resist 3 by aprojection optical system, using quadrupole illumination, whereby thefirst positive photo-resist 3 is exposed (step S12: FIG. 2). In thepresent embodiment, an immersion lithography system having the exposurewavelength (λ) of, for example, 193 nm, and numerical aperture (NA) of,for example, 1.07 is used.

Half-tone phase shift mask 20 has a transparent substrate 11 and ahalf-tone phase shift film 12. Transparent substrate 11 is formed of amaterial transparent to exposure light, so that the exposure light ispassed therethrough. Half-tone phase shift film 12 is formed ontransparent substrate 11 and has a plurality of openings 12 a exposingportions of the surface of transparent substrate. Half-tone phase shiftfilm 12 is formed such that the exposure light transmitted throughhalf-tone phase shift film 12 comes to have the phase different fromthat of the exposure light transmitted through the opening 12 a (forexample, phase different by 180°). Further, optical intensity of theexposure light transmitted through half-tone phase shift film 12relative to the optical intensity of light transmitted through theopening, which is large as compared with the wavelength, that is,transmittance of half-tone phase shift film 12, may be setappropriately, for example, to 20%.

Assume an orthogonal lattice (for example, square lattice) having aplurality of longitudinal lines and a plurality of lateral linesintersecting with each other when viewed two-dimensionally, such asshown in FIG. 12. The plurality of openings 12 a are arranged regularlyat each of the plurality of intersections of the plurality oflongitudinal lines and the plurality of lateral lines, thereby formingthe pattern of dense holes.

Referring to FIG. 6, the first positive photo-resist 3 having theoptical image of a pattern of dense holes exposed as described above isdeveloped. Consequently, a pattern of a plurality of holes 3 a is formedin the first photo-resist 3. Each of the plurality of holes 3 a of thepattern is arranged regularly, by way of example, with the arrangementpitch of 160 nm and the diameter of 60 nm, whereby a pattern of denseholes is formed (step S13: FIG. 2). Though not shown here, when the BARCand TARC films mentioned above are applied, BARC film remains as it isafter development. The remaining BARC film also serves as a BARC film inthe second exposure process described later. The TARC film is dissolvedat the time of development of first photo-resist 3 or by a process priorto development.

Thereafter, a hardening process is performed in which the firstphoto-resist 3 is solidified by volatilizing remaining solvent from thefirst photo-resist 3. The hardening process is performed to avoidmixture of another, second photo-resist 4 applied and formed on thefirst photo-resist 3 in the second exposure process with the firstphoto-resist 3, which mixture hinders formation of a uniform film.Generally, the hardening process is realized by irradiating the firstphoto-resist 3 with ultraviolet ray, irradiation with an electron beam,or injection of rare gas ions. In the present embodiment, the hardeningprocess is performed, for example, by irradiating ultraviolet ray.

Referring to FIG. 7, on the first photo-resist 3 after hardeningprocess, another, second positive photo-resist 4 is applied and formedto fill each of the plurality of holes 3 a of the pattern (step S2: FIG.1). At this time, though not shown, a bottom anti-reflection coating(BARC) and a top anti-reflection coating (TARC) are formed as upper andlower layers of the second positive photo-resist 4 as needed. In thepresent embodiment, the BARC film formed as the lower layer of firstphoto-resist 3 is left as it is and, therefore, BARC film is not formedin this step of forming the second photo-resist 4. The TARC film isnecessary for precise pattern formation and, therefore, it is formed asan upper layer of the second photo-resist 4.

Referring to FIG. 8, the second exposure process is performed. Anoptical image of a high-transmittance half-tone phase shift mask 30having a pattern of randomly arranged holes formed therein is projectedto the second positive photo-resist 4 by a projection optical systemusing a cross-pole illumination, and the second photo-resist 4 isexposed (step S3: FIG. 1). In the present embodiment, immersionlithography system having the exposure wavelength (λ) of, for example,193 nm, and numerical aperture (NA) of, for example, 1.07 is used.

High-transmittance half-tone phase shift mask 30 has a transparentsubstrate 21 and a half-tone phase shift film 22. Transparent substrate21 is formed of a material transparent to exposure light, so that theexposure light is passed therethrough. Half-tone phase shift film 22 isformed on transparent substrate 21 and has one or a plurality ofopenings 22 a exposing a portion or portions of the surface oftransparent substrate 21. Half-tone phase shift film 22 is formed suchthat the exposure light transmitted through half-tone phase shift film22 comes to have the phase different from that of the exposure lighttransmitted through the opening 22 a (for example, phase different by180°). Further, optical intensity of the exposure light transmittedthrough half-tone phase shift film 12 relative to the optical intensityof light transmitted through the opening, which is sufficiently large ascompared with the wavelength, is at least 15% and at most 25%. DimensionW of the opening 22 a is at least 0.26 and at most 0.45 with thewavelength λ/numerical aperture NA=1, and preferably, it is at least0.32 and at most 0.39.

Here, the dimension W of opening 22 a means, if the opening 22 a has asquare shape when viewed two-dimensionally, the dimension of one side ofthe square.

Assume an orthogonal lattice (for example, square lattice) having aplurality of longitudinal lines and a plurality of lateral linesintersecting with each other when viewed two-dimensionally, as shown inFIG. 13. The one or a plurality of openings 22 a are arranged at randomat any of the intersections of the plurality of longitudinal lines andlateral lines, thereby forming a pattern of holes arranged at random.Further, the virtual lattice of FIG. 13 corresponds to the virtuallattice of FIG. 12. Therefore, the positions of openings 22 a of FIG. 13coincide with positions of any of the plurality of holes 12 a of thepattern shown in FIG. 12.

By the exposure using high-transmittance half-tone phase shift mask 30,a dark point image as the bright-dark inverted image of openings 22 a ofhalf-tone shift phase shift film 22 is projected to the secondphoto-resist 4. Specifically, in a common half-tone phase shift mask, aregion where an opening is formed becomes the bright portion while theregion where the half-tone phase shift film is formed becomes the darkportion. In contrast, in the high-transmittance half-tone phase shiftmask 30, the region where opening 22 a is formed becomes the darkportion and the region where high-transmittance half-tone phase shiftfilm 22 is formed becomes the bright portion.

Therefore, by appropriately setting the amount of exposure, the opticalintensity of the dark point image formed by opening 22 a can be set notto dissolve the second positive photo-resist 4 at the time ofdevelopment. Further, optical intensity of exposure light transmittedthrough the region where high-transmittance half-tone phase shift film22 relatively larger than the wavelength is formed comes to besufficient to dissolve the second positive photo-resist 4 at the time ofdevelopment.

Referring to FIG. 9, the second positive photo-resist 4 having the imageof dark points arranged at random exposed as described above isdeveloped, whereby the resist at portions of the dark points is left asa pattern of dots. As a result, the portion corresponding to the dots ofthe pattern of the second photo-resist 4 fill the inside of any of theplurality of holes 3 a of the pattern of the first photo-resist 3. Asthe dot pattern 4 fills hole pattern 3 a, a pattern of holes arranged atrandom when viewed two-dimensionally can be obtained.

Referring to FIG. 10, using photo-resists 3 and 4 as a mask, film 2 tobe processed is selectively removed by etching. Thereafter,photo-resists 3 and 4 are removed, for example, by ashing.

Referring to FIG. 11, by the etching, a pattern of holes 2 a arranged atrandom when viewed two-dimensionally is formed on the film 2 as theobject of processing, and the pattern in accordance with the presentembodiment is formed. The pattern formed in this manner may beapplicable to an electronic device.

Next, the projection aligner used in the first and second exposureprocesses of the pattern forming method above will be described.

Referring to FIG. 14, the projection aligner is to project a pattern onphoto mask 30 (or 20) to the second photo-resist 4 on substrate 1. Theprojection aligner has an illumination optical system from a lightsource 111 to the pattern of photo mask 30 (or 20) and a projectionoptical system from the pattern of photo mask 30 (or 20) to substrate 1.

The illumination optical system includes a light source 111, areflecting mirror 112, a collective lens 118, a fly-eye lens 113, adiaphragm 114 for modified illumination, collective lenses 116 a, 116 b,116 c, a blind diaphragm 115, and a reflecting mirror 117. Theprojection optical system includes projector lenses 119 a, 119 b and apupil plane diaphragm 125.

In the exposure operation, first, a light beam 111 a emitted from lightsource 111 is reflected by reflecting mirror 112. Then, light beam 111 apasses through collective lens 118 and enters each of fly-eye componentlenses 113 a of fly-eye lens 113 and, then, passes through diaphragm114.

Here, light beam 111 b represents an optical path formed by one fly-eyecomponent lens 113 a, and light beam 111 c represents an optical pathformed by fly-eye lens 113. Light beam 111 a that has passed throughdiaphragm 114 passes through collective lens 116 a, blind diaphragm 115and collective lens 116 b, and reflected at a prescribed angle byreflecting lens 117.

Light beam 111 a reflected by reflecting lens 117 passes throughcollective lens 116 c, and uniformly irradiates an entire surface ofphoto mask 30 (or 20) having a prescribed pattern formed thereon.Thereafter, light beam 111 a is reduced to a prescribed magnification byprojector lenses 119 a and 119 b, and exposes the second photo-resist 4on substrate 1.

In the present embodiment, phase shift mask 30 (or 20) is irradiated notby normal illumination but modified illumination both in the first andsecond exposure processes. By normal illumination, the exposure lightirradiates phase shift mask 30 (or 20) vertically as shown in FIG. 15and, by the flux of three light beams of 0-th and ±1-st order,photo-resist of wafer 10 is exposed. When the pattern of phase shiftmask 30 (or 20) becomes smaller, diffraction angle increases and, withvertical illumination, entrance of light beams of ±1-st order to thelens becomes difficult, possibly resulting in resolution failure.

Therefore, modified illumination is used, so that the illuminating lightbeam flux enters obliquely to phase shift mask 30 (or 20), as shown inFIG. 16. Thus, exposures becomes possible only with the flux of twolight beams of 0 and +1-st or −1-st order diffracted by phase shift mask30 (or 20), attaining resolution.

As the modified illumination in the second exposure process of thepresent embodiment, cross-pole illumination is used. Specifically, across-pole illumination diaphragm 114 having four transmitting portions114 a such as shown in FIG. 17 is used as diaphragm 114 of FIG. 14.Further, as the modified illumination for the first exposure process ofthe present embodiment, quadrupole illumination is used. Specifically, aquadrupole diaphragm 114 having four transmitting portions 114 a andhaving the shape of cross-pole illumination rotated by 45° as shown inFIG. 18 is used as diaphragm 114 of FIG. 14.

Next, the structure of an electronic device having a pattern obtained bythe pattern forming method in accordance with the present embodimentwill be described.

The cross-sectional view of FIG. 11 corresponds to the cross-sectiontaken along the line XI-XI of FIG. 19. Referring to FIGS. 11 and 19, anelectronic device in accordance with the present embodiment hassubstrate 1 and film 2 as the object of processing formed on substrate1. In film 2 as the object of processing, a pattern of a plurality ofholes 2 a arranged at random when viewed two-dimensionally is formed.The plurality of holes 2 a of the pattern are arranged at arbitraryintersections 53 among a plurality of intersections 53 where a pluralityof longitudinal lines 51 and a plurality of lateral lines 52 intersect,when we assume an orthogonal lattice (for example, square lattice)having the plurality of longitudinal lines 51 and the plurality oflateral lines 52 intersecting with each other when viewedtwo-dimensionally. Two-dimensional dimension (diameter) of the hole 2 aof the pattern is, by way of example, 60 to 70 nm.

Next, how a bright-dark inverted image of the pattern is obtained byusing high-transmission half-tone phase shift mask 30 shown in FIG. 8will be described. In the description here, the exposure wavelength of248 nm is used, different from the wavelength of 193 nm used in theembodiment. The physical phenomenon, however, is independent of thewavelength and, therefore, it is noted that the same phenomenon occurswith the wavelength of 193 nm.

Referring to FIGS. 20 to 23, the parameter used in each graph is focus.Optical conditions are as follows: exposure light wavelength is 248 nm,numerical aperture NA is 0.80, and illumination is cross-poleillumination (σ_(in)/σ_(out)=0.70/0.85). The shape of diaphragm 14 ofthe cross-pole illumination is as shown in FIG. 17, with four lighttransmitting portions 114 a. Further, transmittance of phase shift mask30 (I2/I1) is 20%.

When the dimension W of opening 22 a of high-transmittance half-tonephase shift mask 30 is large, pattern formation is almost the same asthat by a conventional half-tone phase shift mask. In that case,intensity of light transmitted through opening 22 a is sufficientlyhigher than the intensity of light transmitted through half-tone phaseshift film 22 in a phase relation of canceling, as shown in FIG. 20.Therefore, at a region corresponding to opening 22 a, a portion brighterthan other regions (portion of high optical intensity) is formed.

When the dimension W of opening 22 a is made smaller, intensity of lighttransmitted through opening 22 a becomes lower as shown in FIG. 21, andcancellation by the light transmitted through half-tone phase shift film22 becomes relatively larger. As a result, an image having approximatelythe same intensity as that of light transmitted through half-tone phaseshift film 22 is formed. In that case, the image contrast is low and itbecomes difficult to form a pattern in the photo-resist.

When the dimension W of opening 22 a is further made smaller, intensityof light transmitted through opening 22 a becomes approximately the sameas the intensity of light transmitted through half-tone phase shift film22. Here, the phases have the relation opposite to each other (that is,the phases are different by 180° from each other) and, therefore, at theregion corresponding to the opening 22 a, a dark point imagesufficiently darker than other regions is formed, as shown in FIG. 22.Specifically, a bright-dark inverted image of the pattern of half-tonephase shift film 22 is obtained. When this image is applied to apositive photo-resist, a dot pattern can be formed in the photo-resist.

When the dimension W of opening 22 a is further made smaller, intensityof light transmitted through opening 22 a becomes smaller than theintensity of light transmitted through half-tone phase shift film 22 andthe cancellation effect becomes smaller, as shown in FIG. 23. As aresult, the dark point becomes less dark (brighter).

When the dimension W of opening 22 a is further made smaller, opening 22a would be substantially non-existent, and the image contrast is lost.

It can be seen that, under the optical conditions described above, thebright-dark inverted image such as shown in FIG. 22 is obtained and thedark point image of the bright-dark inverted image has superior focusingcharacteristic. Further, in order to obtain such a bright-dark invertedimage, it is necessary that light transmittance defined as the ratio ofintensity of exposure light transmitted through half-tone phase shiftfilm 22 with respect to the intensity of exposure light transmittedthrough opening 22 a is at least 15% and at most 25%. Further, thedimension W of opening 22 a must be at least 0.26 and at most 0.45 andpreferably at least 0.32 and at most 0.39, when measured with theexposure light wavelength λ/numerical aperture NA being 1. Such relationis described in Japanese Patent Laying-Open No. 2004-251969.

Next, result of inspection of optical images in the first and secondexposure processes will be described.

FIG. 24 is a contour line map representing intensity distribution of anoptical image of a pattern of 112 nm×112 nm holes arranged densely intwo-dimension with a pitch of 160 nm formed on a 20% transmittancehalf-tone phase shift mask 20, in the first exposure process. Opticalconditions are as follows: exposure light wavelength is 193 nm,numerical aperture NA is 1.07, and illumination is quadrupoleillumination (σ_(in)/σ_(out)=0.85/0.95). FIG. 25 represents relativeintensity distribution at positions (spatial positions) along a maincross-section of the dense holes in the first exposure process, usingfocus as a parameter. Referring to FIGS. 24 and 25, the optical imageobtained in the first exposure process has sufficient contrast to attainresist resolution, and superior focusing characteristic with smallvariation with focus. It can be seen that, because of suchcharacteristics of the optical image, a pattern of dense holes havingthe diameter of up to 60 nm and the pitch of 160 nm can be formed in thefirst photo-resist 3 with high margin.

FIG. 26 plots dimension of bright point image formed in the firstexposure process, that is, Image CD (Critical Dimension) with respect tothe focus, using slice level (amount in inverse proportion to the amountof exposure) as a parameter. Referring to FIG. 26, in the first exposureprocess, there is little CD value variation caused by defocus and it canbe seen that superior focusing characteristic can be realized.

FIG. 27 is a contour line map representing intensity distribution of anoptical image of a pattern of 62 nm×62 nm holes formed on a 20%transmittance half-tone phase shift mask 30, in the second exposureprocess. Optical conditions are as follows: exposure light wavelength is193 nm, numerical aperture NA is 1.07, and illumination is cross-poleillumination (σ_(in)/σ_(out)=0.60/0.80). The hole pattern of 62 nm×62 nmis arranged corresponding to a position of a part of the pattern ofholes formed in the first photo-resist 3. Referring to FIG. 27, in theoptical image, portions corresponding to the pattern of holes on the 20%transmittance half-tone phase shift mask 30 appear as dark point imagesbecause of phase cancellation.

Because of the dark point image, the second positive photo-resist 4 atthe corresponding portion is not dissolved at the time of developmentand, therefore, the second photo-resist 4 of this portion (dot patternportion) is left after development. Consequently, part of the pluralityof holes of the pattern formed in photo-resist 3 as an underlying layeris plugged by the dot pattern portion of the second photo-resist 4. Thisis the purpose of the second exposure process.

FIG. 28 is a contour line map representing intensity distribution of anoptical image of a pattern of 62 nm×62 nm holes formed under theabove-described optical conditions on a 20% transmittance half-tonephase shift mask 30, in the second exposure process. The hole pattern of62 nm×62 nm is arranged corresponding to all the holes of the patternexcept for one hole, among the pattern of plurality of holes formed inthe first photo-resist 3. Referring to FIG. 28, in the optical image,the portions corresponding to the pattern of holes on the 20%transmittance half-tone phase shift mask 30 are dark portions because ofphase cancellation, while the portion free of any hole pattern on mask30 is a bright portion. Specifically, in the patterning of the secondphoto-resist 4 using mask 30, all the holes except for one hole of thepattern of dense holes formed in the first photo-resist 3 are plugged bythe pattern of dots of the second photo-resist 4 formed by the darkpoint image. In this manner, a pattern of isolated hole can be formed inthe film 2 as the object of processing.

FIGS. 29 and 30 plot optical image intensity at a portion free of anyhole (FIG. 29) and at a portion with isolated hole (FIG. 30) of the maskused in the second exposure process, using focus as a parameter. In thefigure, image intensity (slice level: adjusted by the amount ofexposure) as the border as to whether the resist is dissolved or not, isshown by a dotted line.

Referring to FIGS. 29 and 30, both the dot pattern portion (plug formedportion) where the holes are non-existent and the dot pattern portion(plug formed portion) where the isolated hole exists are sufficientlydark for resist resolution. Further, variation of optical intensity withfocus is small. Specifically, it is expected that formation of a dotpattern with sufficient process margin is possible by exposing theoptical image. Further, at the hole pattern portion where the isolatedhole exists, a bright point image having sufficient intensity to causereaction of the second photo-resist 4 is formed.

From the foregoing, it is understood that by the present embodiment, apattern of dense holes can be formed in the first positive photo-resist3 using half-tone phase shift mask 20 and modified illumination in thefirst exposure process. Thereafter, in the second exposure process, byan image of dark points arranged at random formed by using hightransmittance half-tone phase shift mask 30 and cross-pole illumination,part of the holes 3 a of the pattern of dense holes formed in the firstexposure process can arbitrarily be filled by the pattern of dotsprovided by the second photo-resist 4. Accordingly, the pattern ofrandomly arranged holes can be formed. Thus, it becomes possible tosimultaneously form a pattern of dense holes with very small pitch and apattern of random arrangement including an isolated hole, of minutedimensions, which could not be formed by the conventional method.

Embodiment 2

The present embodiment differs from Embodiment 1 in that cross-poleillumination shown in FIG. 17 is used as the modified illumination ofthe first exposure process shown in FIG. 5. When the cross-poleillumination is used for the first exposure process, holes 12 a in thepattern of dense holes of half-tone phase shift mask 20 shown in FIG. 5have the arrangement pitch P1 of, for example, 120 nm andtwo-dimensional dimension is, for example, 88 nm×88 nm. Further, holes 3a of the pattern of dense holes in the first photo-resist 3 formed byusing half-tone phase shift mask 20 have the arrangement pitch of, forexample, 120 nm, and the diameter of, for example, 60 nm.

Except for this point, the method of pattern formation and the structureof electronic device of the present embodiment are substantially thesame as those of Embodiment 1 and, therefore, description thereof willnot be repeated.

Next, results of inspection of the optical images in the first andsecond exposure processes of the present embodiment will be described.

FIG. 31 is a contour line map representing intensity distribution of anoptical image of a pattern of 88 nm×88 nm holes arranged densely intwo-dimension with a pitch of 120 nm on a 20% transmittance half-tonephase shift mask 20, in the first exposure process. Optical conditionsare as follows: exposure light wavelength is 193 nm, numerical apertureNA is 1.07, and illumination is cross-pole illumination(σ_(in)/σ_(out)=0.70/0.80). FIG. 32 represents relative intensitydistribution at positions (spatial positions) along a main cross-sectionof the dense holes in the first exposure process, using focus as aparameter. Referring to FIGS. 31 and 32, the optical image obtained inthe first exposure process has sufficient contrast to attain resistresolution, and superior focusing characteristic with small variationwith focus. It can be seen that, because of such characteristics of theoptical image, a pattern of dense holes having the diameter of up to 60nm and the pitch of 120 nm can be formed in the first photo-resist 3with high margin.

FIG. 33 plots dimension of bright point image formed in the firstexposure process, that is, Image CD with respect to the focus, usingslice level as a parameter. Referring to FIG. 33, in the first exposureprocess, there is little CD value variation caused by defocus and it canbe seen that superior focusing characteristic can be realized.

FIG. 34 is a contour line map representing intensity distribution of anoptical image of a pattern of 54 nm×54 nm holes formed on a 20%transmittance half-tone phase shift mask 30, in the second exposureprocess. Optical conditions are as follows: exposure light wavelength is193 nm, numerical aperture NA is 1.07, and illumination is cross-poleillumination (σ_(in)/σ_(out)=0.60/0.80). The hole pattern of 54 nm×54 nmis arranged corresponding to a position of a part of the pattern ofholes formed in the first photo-resist 3. Referring to FIG. 34, in theoptical image, portions corresponding to the pattern of holes on the 20%transmittance half-tone phase shift mask 30 appear as dark pointsbecause of phase cancellation.

Because of the dark point image, the second positive photo-resist 4 atthe corresponding portion is not dissolved at the time of developmentand, therefore, the second photo-resist 4 of this portion (dot patternportion) is left after development. Consequently, part of the pluralityof holes of the pattern formed in photo-resist 3 as an underlying layeris plugged by the dot pattern portion of the second photo-resist 4. Thisis the purpose of the second exposure process.

FIG. 35 is a contour line map representing intensity distribution of anoptical image of a pattern of 54 nm×54 nm holes formed under theabove-described optical conditions on a 20% transmittance half-tonephase shift mask 30, in the second exposure process. The hole pattern of54 nm×54 nm is arranged corresponding to all the holes of the patternexcept for one hole, among the pattern of plurality of holes formed inthe first photo-resist 3. Referring to FIG. 35, in the optical image,the portions corresponding to the pattern of holes on the 20%transmittance half-tone phase shift mask 30 are dark portions because ofphase cancellation, while the portion free of any hole pattern on mask30 is a bright portion. Specifically, in the patterning of the secondphoto-resist 4 using mask 30, all the holes except for one hole of thepattern of dense holes formed in the first photo-resist 3 are plugged bythe pattern of dots of the second photo-resist 4 formed by the darkpoint image. In this manner, a pattern of isolated hole can be formed inthe film 2 as the object of processing.

FIGS. 36 and 37 plot optical image intensity at a portion free of anyhole (FIG. 36) and at a portion with isolated hole (FIG. 37) of the maskused in the second exposure process, using focus as a parameter. In thefigure, image intensity (slice level: adjusted by the amount ofexposure) as the border as to whether the resist is dissolved or not, isshown by a dotted line.

Referring to FIGS. 36 and 37, both the dot pattern portion (plug formedportion) where the holes are non-existent and the dot pattern portion(plug formed portion) where the isolated hole exists are sufficientlydark for resist resolution. Further, variation of optical intensity withfocus is small. Specifically, it is expected that formation of a dotpattern with sufficient process margin is possible by exposing theoptical image. Further, at the hole pattern portion where the isolatedhole exists, a bright point image having sufficient intensity to causereaction of the second photo-resist 4 is formed.

From the foregoing, it is understood that by the present embodiment, apattern of dense holes can be formed in the first positive photo-resist3 using half-tone phase shift mask 20 and modified illumination in thefirst exposure process. Thereafter, in the second exposure process, byan image of dark points arranged at random formed by using hightransmittance half-tone phase shift mask 30 and cross-pole illumination,part of the holes 3 a of the pattern of dense holes formed in the firstexposure process can arbitrarily be filled by the pattern of dotsprovided by the second photo-resist 4. Accordingly, the pattern ofrandomly arranged holes can be formed. Thus, it becomes possible tosimultaneously form a pattern of dense hole patterns with very smallpitch and a pattern of random arrangement including an isolated hole, ofminute dimensions, which could not be formed by the conventional method.

Embodiment 3

The present embodiment differs from Embodiment 1 in that the mask layerin the flowchart of FIG. 1 is a hard mask. In the following, an examplein which the mask layer of the flowchart of FIG. 1 is a hard mask willbe specifically described.

Referring to FIG. 39, first, the film 2 as the object of processing isformed on a substrate (for example, a wafer) 1. On the film 2 as theobject of processing, a hard mask layer 5 is formed (step S21: FIG. 38).Hard mask layer 5 is formed of a material different from the resistmaterial. For example, it is formed of a silicon nitride film.

Referring to FIG. 40, on hard mask 5, a first positive photo-resist 3 isapplied and formed (step S22: FIG. 38). At this time, though not shown,a bottom anti-reflection coating (BARC) and a top anti-reflectioncoating (TARC) are formed as upper and lower layers of the firstpositive photo-resist 3, as needed.

Referring to FIG. 41, the first exposure process is performed. Anoptical image of a 20% transmittance half-tone phase shift mask 20having a pattern of dense holes formed therein is projected to the firstpositive photo-resist 3 by a projection optical system, using quadrupoleillumination, whereby the first positive photo-resist is exposed (stepS23: FIG. 38). In the present embodiment, an immersion lithographysystem having the exposure wavelength (λ) of, for example, 193 nm, andnumerical aperture (NA) of, for example, 1.07 is used.

The structure of half-tone phase shift mask 20 is substantially the sameas that of half-tone phase shift mask 20 in accordance with Embodiment 1and, therefore, description thereof will not be repeated.

Referring to FIG. 42, the first positive photo-resist having the opticalimage of a pattern of dense holes exposed as described above isdeveloped. Consequently, a pattern of a plurality of holes 3 a is formedin the first photo-resist 3. Each of the plurality of holes 3 a of thepattern is arranged regularly, by way of example, with the arrangementpitch of 160 nm and the diameter of 60 nm, whereby a pattern of denseholes is formed (step S24: FIG. 38).

Referring to FIG. 43, using the first photo-resist having the pattern ofdense holes as a mask, the BARC film and hard mask layer 5 areselectively removed by dry etching. Thereafter, the first photo-resist 3is fully separated and removed together with the BARC film.

Referring to FIG. 44, a pattern of dense holes having a plurality ofholes 5 a arranged regularly is formed in hard mask layer 5 (step S25:FIG. 38).

Referring to FIG. 45, on hard mask layer 5 having the pattern of denseholes formed therein, the second positive photo-resist 4 is applied andformed to fill each of the plurality of holes 5 a of the pattern (stepS2: FIG. 1). At this time, though not shown, a bottom anti-reflectioncoating (BARC) and a top anti-reflection coating (TARC) are formed asupper and lower layers of the second positive photo-resist 4 as needed.The TARC film is necessary for precise pattern formation and, therefore,it is also applied in the process for forming the second photo-resist 4.

Referring to FIG. 46, the second exposure process is performed. Anoptical image of a high-transmittance half-tone phase shift mask 30having a pattern of randomly arranged holes formed therein is projectedto the second positive photo-resist 4 by a projection optical systemusing a cross-pole illumination, and the second photo-resist 4 isexposed (step S3: FIG. 1). In the present embodiment, immersionlithography system having the exposure wavelength (λ) of, for example,193 nm, and numerical aperture (NA) of, for example, 1.07 is used.

The structure of high-transmittance half-tone phase shift mask 30 issubstantially the same as that of the high-transmittance half-tone phaseshift mask 30 in accordance with Embodiment 1 and, therefore,description thereof will not be repeated.

In the exposure using high-transmittance half-tone phase shift mask 30,the bright-dark inverted image of the pattern of half-tone phase shiftfilm 22 is projected to the second photo-resist 4. Specifically, in anordinary half-tone phase shift mask, the region where the half-tonephase shift film is formed becomes the dark portion and the region wherethe opening is formed becomes the bright portion, whereas in the case ofthe high-transmittance half-tone phase shift mask 30, the region wherehigh transmittance phase shift film 22 is formed becomes the brightportion and the region where opening 22 a is formed becomes the darkportion.

Therefore, the exposure light transmitted through the region wherehigh-transmission half-tone phase shift film 22 relatively larger thanthe wavelength is formed comes to have such an optical intensity thatdissolves the second positive photo-resist 4 at the time of development.The exposure light transmitted through opening 22 a comes to have suchan optical intensity that does not dissolve the second positivephoto-resist 4 at the time of development.

Referring to FIG. 47, the second positive photo-resist 4 having theimage of randomly arranged dark points exposed as described above isdeveloped. Consequently, the portions of dark point image of the secondphoto-resist 4 are left as a pattern of dots 4 in some of the pluralityof holes 5 a of the pattern of hard mask layer 5 (step S4: FIG. 1). Asthe dots 4 of the pattern fill holes 5 a of the pattern, a pattern ofholes arranged at random when viewed two-dimensionally can be obtained.

Referring to FIG. 48, using the second photo-resist 4 and hard masklayer 5 as a mask, the film 2 as the object of processing is selectivelyremoved and patterned by etching (step S5: FIG. 1). Thereafter, thefirst photo-resist 3 is removed, for example, by ashing, and hard masklayer 5 is removed, for example, by etching.

Referring to FIG. 49, by the etching, a pattern of holes 2 a arranged atrandom when viewed two-dimensionally is formed on the film 2 as theobject of processing, and the pattern in accordance with the presentembodiment is formed. The pattern formed in this manner may beapplicable to an electronic device.

The structure of the electronic device having the pattern obtainedthrough the pattern forming method in accordance with the presentembodiment is substantially the same as that of the electronic device inaccordance with Embodiment 1 shown in FIG. 19 and, therefore,description thereof will not be repeated.

The results of inspection of optical images in the first and secondexposure processes of the present embodiment are approximately the sameas those of Embodiment 1 shown in FIGS. 24 to 30 and, therefore,description thereof will not be repeated.

From the foregoing, it is understood that by the present embodiment, apattern of dense holes can be formed in the first positive photo-resist3 using half-tone phase shift mask 20 and modified illumination in thefirst exposure process. Further, using the first photo-resist 3 as amask, a pattern of dense holes can be transferred to the hard mask layer5. Thereafter, in the second exposure process, by an image of darkpoints arranged at random formed by using high transmittance half-tonephase shift mask 30 and cross-pole illumination, part of the holes 5 aof the pattern of dense holes in the hard mask layer 5 can arbitrarilybe filled by the pattern of dots provided by the second photo-resist 4.Accordingly, the pattern of randomly arranged holes can be formed. Thus,it becomes possible to simultaneously form a pattern of dense holepatterns with very small pitch and a pattern of random arrangementincluding an isolated hole, of minute dimensions, which could not beformed by the conventional method.

Embodiment 4

The present embodiment differs from Embodiment 3 in that cross-poleillumination shown in FIG. 17 is used as the modified illumination inthe first exposure process shown in FIG. 41. When the cross-poleillumination is used for the first exposure process, holes 12 a in thepattern of dense holes of half-tone phase shift mask 20 shown in FIG. 41have the arrangement pitch P2 of, for example, 120 nm andtwo-dimensional dimension is, for example, 88 nm×88 nm. Further, holes 3a of the pattern of dense holes in the first photo-resist 3 formed byusing half-tone phase shift mask 20 have the arrangement pitch of, forexample, 120 nm, and the diameter of, for example, 60 nm.

Except for these points, the method of pattern formation and thestructure of electronic device of the present embodiment aresubstantially the same as those of Embodiment 3 and, therefore,description thereof will not be repeated.

The results of inspection of optical images in the first and secondexposure processes of the present embodiment are approximately the sameas those of Embodiment 2 shown in FIGS. 31 to 37 and, therefore,description thereof will not be repeated.

From the foregoing, it is understood that by the present embodiment, apattern of dense holes can be formed in the first positive photo-resist3 using half-tone phase shift mask 20 and modified illumination in theexposure process. Further, using the first photo-resist 3 as a mask, apattern of dense holes can be transferred to the hard mask layer 5.Thereafter, in the second exposure process, by an image of dark pointsarranged at random formed by using high transmittance half-tone phaseshift mask 30 and cross-pole illumination, part of the holes 5 a of thepattern of dense holes in the hard mask layer 5 can arbitrarily befilled by the pattern of dots provided by the second photo-resist 4.Accordingly, the pattern of randomly arranged holes can be formed. Thus,it becomes possible to simultaneously form a pattern of dense holepatterns with very small pitch and a pattern of random arrangementincluding an isolated hole, of minute dimensions, which could not beformed by the conventional method.

As described above, the pattern forming method in accordance withEmbodiments 1 to 4 described above is to solve the problems of the priorart and to enable formation of a pattern of minute holes arranged atrandom, using a positive photo-resist.

In the pattern forming method in accordance with Embodiments 1 to 4described above, pattern formation is continuously performed twice,whereby formation of a pattern having minute holes arranged at randomusing positive photo-resist becomes possible.

Further, in the pattern forming method in accordance with Embodiments 1to 4 described above, by applying modified illumination in the firstexposure process and by applying the bright-dark inverted image obtainedby high-transmittance half-tone phase shift mask together with modifiedillumination in the second exposure process, pattern formation with highprocess margin becomes possible.

Further, in the pattern forming method in accordance with Embodiments 1to 4 described above, by applying modified illumination in the firstexposure process and by applying the bright-dark inverted image obtainedby high-transmittance half-tone phase shift mask together with modifiedillumination in the second exposure process, pattern formation notrequiring optical proximity correction (OPC) becomes possible.

Further, in the pattern forming method in accordance with Embodiments 1to 4 described above, by applying modified illumination in the firstexposure process and by applying the bright-dark inverted image obtainedby high-transmittance half-tone phase shift mask together with modifiedillumination in the second exposure process, formation of a patternhaving minute holes arranged at random through exposure with smallnumerical aperture (NA) becomes possible. This enables application of aninexpensive exposure machine and the cost of processing can be reduced.

Further, in the method of pattern formation in accordance withEmbodiments 1 to 4 described above, cross-pole illumination is used inthe second exposure process. Therefore, the optical image obtained inthe second exposure process comes to have sufficient contrast to resolvethe resist and superior focusing characteristic with small variationwith focus. This point will be described in the following. In thedescription here, the exposure wavelength of 248 nm is used, differentfrom the wavelength of 193 nm used in the embodiment. The physicalphenomenon, however, is independent of the wavelength and, therefore, itis noted that the same phenomenon occurs with the wavelength of 193 nm.

FIGS. 50A, 50B and 50C include plan views showing the shapes ofdiaphragms of (FIG. 50A) annular illumination, (FIG. 50B) cross-poleillumination and (FIG. 50C) quadrupole illumination to find optimizationof illumination shape for square lattice arrangement, and variations ofoptical images formed by an image forming system with respect todimension W (120 nm-90 nm) of opening pattern 22 a, when pitch P ofopenings 22 a of high-transmission half tone phase shift mask shown inFIG. 8 is changed. In each graph, focus is used as the parameter.

Referring to FIGS. 50A, 50B and 50C, for annular illumination,σ_(in)/σ_(out)=65/80, and for cross-pole illumination and quadrupoleillumination, σ_(in)/σ_(out)=60/80. Further, for cross-poleillumination, the directions of the diagonal of illumination openingdiaphragm (X and Y directions in the figure) are aligned with thedirections of the longitudinal and lateral directions of virtualorthogonal lattice shown in FIG. 13. Further, for quadrupoleillumination, the directions of the diagonal of illumination openingdiaphragm (X and Y directions in the figure) are inclined by 45° fromthe directions of the longitudinal and lateral directions of virtualorthogonal lattice shown in FIG. 13.

As a result, it can be seen that, regardless of the arrangement pitch Pof the openings of half-tone phase shift film 22, superior focusingcharacteristic with small variation with focus can be attained bycross-pole illumination, as compared with annular illumination orquadrupole illumination.

Specifically, by the high-transmittance half-tone phase shift mask 30shown in FIG. 8, superior characteristic can be attained even whenisolated pattern and dense pattern are mixed.

Referring to FIG. 51, the meanings of “isolated pattern” and “densepattern” will be described. Referring to FIG. 51, if there is no patternwithin a distance corresponding to radius R1 of 3 from the center of apattern 2 a when measured with numerical aperture NA/wavelength λ being1, the pattern is referred to as an isolated pattern. If there isanother pattern 2 a within a distance corresponding to radius R2 of 1from the center of one pattern 2 a when measured with numerical apertureNA/wavelength λ being 1, the pattern is referred to as dense patternincluding a plurality of patterns.

Though a method of manufacturing a semiconductor device has beendescribed by way of example of the pattern forming method, the presentinvention is similarly applicable to the method of manufacturing otherelectronic devices such as a liquid crystal display device, a thin filmmagnetic head and the like.

The present invention is particularly advantageous when applied to thestep of forming a hole pattern in forming very fine, advancedsemiconductor integrated circuits.

Further, the effect of the pattern forming method in accordance with thepresent invention is believed to be best utilized when applied mainly tomanufacturing of logic integrated circuit among the advancedsemiconductor integrated circuits.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

1-14. (canceled)
 15. An electronic device manufactured by a method,comprising the steps of: forming a mask layer having a dense holepattern with a plurality of holes positioned densely, on a film as anobject of processing, by applying a first positive photo-resist; forminga second positive photo-resist on said mask layer to fill each of saidplurality of holes of said dense hole pattern; projecting and exposingan image of dark points to said second positive photo-resist using ahalf-tone phase shift mask; developing said exposed second positivephoto-resist to leave a pattern of dots formed at portions of said imageof dark points of said second positive photo-resist in any of saidplurality of holes of the pattern of said mask layer; and patterningsaid film as the object of processing, using said mask layer and saidpattern of dots formed on said second positive photo-resist as a mask;wherein said half-tone phase shift mask has a half-tone phase shift filmhaving an opening formed at a portion of said dot pattern; and in saidstep of projecting and exposing said image of dark points to said secondpositive photo-resist using said half-tone phase shift mask, exposure isperformed such that exposure light transmitted through said half-tonephase shift mask at a region where said opening does not exist hasoptical intensity sufficient to dissolve said second positivephoto-resist at the time of development and optical intensity of saidimage of dark points formed at the portion of said pattern of dots bysaid opening is insufficient to dissolve said second positivephoto-resist at the time of development.
 16. The electronic deviceaccording to claim 15, having a film as an object of processing, whereinassuming a lattice having a plurality of longitudinal lines and aplurality of lateral lines intersecting with each other when viewedtwo-dimensionally, said film as the object of processing has a holepattern at an arbitrary one of the plurality of intersections of theplurality of longitudinal lines and a plurality of lateral lines.